Electrothermal indicating apparatus



April 13, 1937. T, s K 2,076,678

ELECTROTHERMAL INDICATING APPARATUS Original Filed April 21, 1930 2 Sheets-Sheet l INVENTOR. fig. Theodore J Smu/s/li.

I W W ATTORNEY.

April 13, 1937. ,1". J. SMULSKI V 2,076,673

I ELECTROTHERMAL INDICA'i'ING APPARATUS 2 Sheets-Shet 2 Original Filed April 21, 1950 INVENTOR. Theodore JSmuls fi ATTORNEY.

55 of a compensated Patented Apr. 13, 1937* PATENT OFFICE nrnc'rno'rnnmmr. mnrcn'rma Arma a-Us Theodore J. Smnlski, Gary, Ind., assignor to The Anderson Company, Gary,

ollndiana Ind., a. corporation Original application April 21, 1930, Serial No. 445,994. Divided and this application August 26, 1935, Serial No. 37,875

10 Claims.

My invention relates to electro-thermal apparatus and relates particularly to electro-thermal apparatus adapted for operation in pairs comprising a controlled and control apparatus for 5 any useful purpose wherein simultaneous commensurable operation of a controlling and controlled apparatus is required.

The apparatus of my invention is directed particularly to controlled apparatus, such as apparatus for indicating a physical condition, as temperature, and is divisional of my co-pending application Serial No. 445,994, filed April 21, 1930,

for Electro-thermostatic apparatus, the apparatus of iny co-pending application being directed primarily to controlling apparatus.

It is an object of mypresent invention to provide improved, efilcient controlled apparatus operable simultaneously and commensurably to controlling apparatus to indicate a physical condition.

Another object of my invention is to provide an improved indicating apparatus for receiving electrical impulses from a controlling apparatus, the impulses being telegraphed. thereto commensurably to the temperature of a body with which the controlling apparatus is associated.

Another object of my invention is to provide an improved electro-thermal apparatus wherein the thermal properties of the apparatus may be eihciently predetermined in quantity production of the apparatus. 1

Another object of my invention is to provide improved apparatus for indicating temperatures remotely from the manifestation of the temperature effect to be indicated.

Other objects of my in' tion and the invention itself will become increasingly apparent from v a consideration of the following description and drawings, wherein:

mechanism which may be advantageously employed in said system embodying my invention;

Fig. 2 is a plan view of the mechanism of Fig. 1, the view showing the indicator dial and mov- 45 able hand therefor;

Fig. 3 is a side elevational view of the indicat ing mechanism of Fig. 1, taken from a right angle position relative to Fig. 1;

Fig. 4 is a bottom plan view of an insulating 50 mounting plate for the said indicator mecha- Fig. 5 is a section taken along the line 5-5 of Fig.

Fig. .6 is a longitudinal medial sectional view thermostat mechanism and of a controlling apparatus which is another em- Fig. 1 is a side elevational view of an indicator heating element therefor, together with associated parts relating to the indicating apparatus 01 Figs. 1 to 5 inclusive;

Fig. "4 is an elevational view partially in section of a controlling apparatus embodying the 5 principle of my invention;

Fig. 8 is a longitudinal medial sectional view githe apparatus of Fig. 7 taken along the line Fig. 9 is an end elevational view of the controlling apparatus of Fig. 7, with the cover cap therefor removed;

Fig. 10 is a top plan view of the apparatus of Fig. 7 with the cover cap in position;

Fig. 11 is a diagrammatic view of the controlling and controlled apparatus of the foregoing figures, and an operative electrical system in which such apparatus is included; Figs. 12 and Bare front elevational and longitudinal medial sectional views, respectively, of an indicating apparatus which is another embodiment of my invention;

Figs. 14 and 15 are front elevational and longitudinal medial sectional views, "respectively, of-a further modification of my invention, with the front dial plate and casing removed;

Figs. 16 and 17 are views similar to Figs. 14 and 15 respectively, illustrating a further; embodiment of my invention;

Fig. 18 is a section with parts omitted taken on the line l8-I8 of Fig. 17 showing an adjustable operative element of the mechanism of Figs. 16 and 17;

Fig. 19 is a longitudinal medial sectional view 35 bodiment of my invention;

Fig. 20 is a section taken along the line 20-20 of Fig. 19; and Fig. 21 is a side elevational view of an operative element of the apparatus of Fig; 11.

,Referring now to Figs- 1 to 6, inclusive, in which a form of the indicating mechanism of the system is illustrated, the parts shown may be mounted on a mounting plate IQ of insulating material. A pair of posts I! secured to and extending in parallel relation from the support I! carry a plate 20 secured to the posts by screws 2|. Th dial plate, preferably, is marked with dial mam-1e22, some of the spaced marked 5 divisions thereof'being provided with numerals, which may, for instance, refer to degrees of temperature, Fahrenheit. The pointer hand 43 is supported by a thermostat comprising a pair of reversely coiled helices 23 and 14, which are r integrally joined together by the contiguous ends 25.'of the helices disposed in the form of a loop.

The two helices are axially aligned and preferably longitudinally spaced with a baille plate 26 of heatinsulating material, preferably disposed between the two to restrain the flow of heated air from the helix 24 to the helix 23, and from the heating element 21 which is axially disposed within the helix 24 for the purpose of heating, it when the device is in operation as later herein described.

The baille plate 26 is supported on a bracket 31 which is rigidly secured on the insulating base l8 by a screw 38 projected through the base of said bracket and said plate. The nuts 33 on the outermost'end of the screw 38 provide a binding post for making connection by circuit conductors with the screw-38 and therefore with the bracket 31 to which a terminal of the heating element 21 is permanently connected.

The pointer 43 is secured to the outermost coil of the helix 23 in any suitable manner, such as by soldering the disk 28 to the center of which the pointer 43 is aflixed, to the outermost convolution of the helix, or by effecting a frictional engagement therebetween. The hand 43 is joined to the disk 28 by a short arm I I2 of the hand projected through an arcuate opening 6| of the dial H plate. The remote end of the helix'24 terminates in a convolution 29, preferably formed as an an-' nulus and rigidly aflixed to a hollow screw 30 which is-screwthreaded within the bore 3| of the insulating supporting plate l8. The screw 3| may have a screw driver receiving slot as shown at 32.

The heating element 21 is axially suspended within the helix 24, being in the form of a resistance wire helix and is maintained in position by its leading-in wires 33 and 34 projected through the axial bore of a bored insulating plug 35 and an axially disposed aperture 36 of the baflie plate A preferably copper circuit conductor 40 of substantial gauge and a like circuit conductor- 4| are joined to the leading-in wires 33 and 34, respectively, and are connected to the similar binding posts 42 and 39, respectively, the latter'through the bracket 31 to which the conductor 4| is preferably connected.

From the foregoing description, it will be understood that the helices 23 and 24 being oppositely wound and alike in the number of their convolutions and other dimensional characteristics and each being formed of a ribbon of bi-metallic material, upon changes of temperature will tend to wind or unwind, in a manner well known for such helices, but in opposite directions and to the same degree, whereby for all ambient temperatures, any tendencies toward rotative movement of the hand 43 resulting from such changes of temperature will be thoroughly compensated, each of the helices compensating for the other.

However, only the helix 24 is exposed to the effect of electrical heating, being provided with the electrical heating element 21 axially telescoped within it, and heat therefrom substantially being prevented as by the guard 26 from reaching the helix 23. When the heating element 21 is energized, the helix will tend to unwind to produce a rotative movement of its arm 25 and therefore of the carried helix 23 which supports the hand supporting disk 28. As a result of this electrical heating action, the hand 43 will advance along the scale 22 toward the right from its starting position at the left side of the dial.

In calibrating the instrument, should it be found that the heating helix 21 produces more than the predetermined amount of heat, and therefore deflects the needle 43 to an excessive degree, the portion of the helix 21 disposed within the thermostat helix 24 may be reduced by grasping the circuit conductor 40 with a suitable tool and pulling the leading-in wire 33 to draw some of the wire of the heating element 21 into and/or through the bore of the insulating plug 36 to reduce the length of the heating element disposed within the thermostat helix. Such an adjustment may be employed where great accuracy is required and as a final adjustment.

The helix 21 is preferably wound with considerable closeness between the successive convolutions which are of a small diametrical dimension so that the mass of the heating element per cubic inch'of space occupied is relatively large. This arrangement is conducive to the provision of a substantial amount of heat storage capacity in the helix 21, whereby the helix will not rapidly lose its heat between impulses of heating electrical current directed through the helix.

Referring now to the controller of Figs. 7 to 11 inclusive, and Fig. 21, the controller, preferably, provides a metal tubular heat conducting support having a hexagonal head I, a reduced intermediate portion 2 and a longitudinally extending tubular tip 3 having an integral end closure 4. The bore 5 of the support extends axially therethrough and is of such a diameter as to receive the double thermostatic element of Fig. 21 telescoped preferably axially therein with its annular end 6 integrally united as by solder 1 to the metal end 4 of the support with the outer surfaces of its convolutions disposed in substantial air spaced relation to the inner walls of the tubular support. The helical thermostat is formed of a strip of thermostatic bi-metallic material, the one section of which comprises a metallic strip of a metal having a different coeflicient of thermal expansion than the second section which is integrally secured to the first section,

The composite strip thus formed is given the form of a helix having longitudinally aligned sections, each section of which is reversely wound relative to the direction of winding of the other.

One of the sections, namely the section 6 terminating in the annulus 6, as above stated, is relatively longer, contains more convolutions, and the total length of bi-metallic strip forming said convolutions is greater than the number of convolutions and the aggregate length of the convolutions of section 9, 'for a purposelater explained. The sections are integrally joined together by a substantially U-shaped portion of the strip shown at l0, which is stiffened against bending by providing it with an out-turned tip H, see especially Fig. 21.

To the end convolution |2 of the shorter thermostat section 9, formed as described, a pair of diametrically oppositely disposed prongs I6 are preferably provided to which, as shown in Figs.

7, 8, 9, and 11, a metallic cross arm I4 is soldered and projects laterally to one side of the two prongs to terminate in a contact carrying arm l6 supporting an electrical contact element l1.

Prior to placement of the cross arm |4 on'the prongs, a disk 43 of preferably electrical and heat insulating material is aflixed to the hexagonal head of the tubular support by the provision of a tubular flange 44 whose bore is of the same diameter as the bore 5, projecting integrally from said head and terminating in a slightly outturned end 45. Forced into the material of the insulating disk 43 is preferably a metal washer 46 75 fitted over the flange 44. Prior .'to expanding its end 44 to the form shown, the disk 43 is circumferentially relieved near its outer end for the rethreaded recesses of-the disk 43 torigldly secure the cap 48 on the disk.

Supported on the inner face of the disk 43 I provide a tube- 59 of glass or other heat resistant material secured to the disk by press fitting its end into a centrally disposed recess of the inner wall of the disk. In longitudinal alignment and communicating with the bore of the glass tube 58 I provide a passage 52 extending from the'bore of the tube 59 to the opposite surface of the disk for.

the reception of an electrical circuit conductor 53 projected through said passage 52 and through the longitudinal bore of the glass tube 58 to its free end where the conductor 53 is reversely turned and connects, integrally or otherwise, with the heat producing'electrlcal circuit conductor 54,

helically wrapped fromthe free end of the tube 50 toward its fixed end on its outer surface.=

The glass tube 50 is of such reduced diameter relative to the internal bore of the shorter helix 9,

as' to be substantially air spaced therefrom along the length of the tube, and therefore the length of the heating element winding 54 wrapped about the tube 50, is preferably somewhat less than the length of the helix 9. In preparing the helices 8 and 9, I preferably make the innermost material that which has the greatest coeflicient of thermal disk 43, said post, preferably, projecting into the Y material of the disk by a stem portion, not shown.

The post supports a contact screw 55, screw-- threaded transversely through it, said screw being provided with a tip contact 56, on its end adapted for engagement with the movable contact l1 carried by the contact arm 16. By turning the screw 55 the fixed contact 56 may be adjusted relative to a given position of the movable contact l1 so as to vary the rotative position of engagement between said contacts.

A bridge 51 secured at its ends to the disk 43 by screws 58 overlies the center of the disk, and also the cross arm l4. The cross arm 14 carries a pinion rod 59, disposed in axial alignment with the axis of the helices 8 and 9, which projects through a journal opening 6| extending centrally through the bridge 51. 1

In this manner, the helices 8 and 9 and the contact carrying arm l8 are held in proper position relative to the axis of the device, the cross-. arm l4, which terminates in the contact arm 11 A binding post so is rigidly mounted in the 111-.

' sulating material of the disk 43, and projects The operation of the controller, above described, will be readily understood by reference to the figures described and by collateral reference to Fig. 11, showing diagrammatically an electrical system in which the indicator apparatus of Figs. 1 to .6 is shown as included, and operable under the control of the described controller. The system and apparatus. operate as follows: It being understood that the tubular support is screwthreaded by its exteriorly threaded intermediate portion 2 into a wall of a fluid conduit, the variable temperature of the fluid contained therein being that variable factor, the quantitative values of which are desired to be indicated remotely of the controller at the indicator having the indicating hand or needle 43, with the closed tubular end 3 projecting into said fluid.

For example, it may be assumed that the tubular end 3 is thus projected into the cooling water of an automotive engine water cooling jacket and the temperature of such water is thermally conducted by the end wall 4 of the tube to the annular end '8 of the bi-metal helix 8, which is thereby heated to a temperature approximately that of the temperature of water in the jacket. The temperature of the water or other fluid in L contact with the tip 3 of the support is communicated to the interior thereof and will heat the helices 8 and 9. The helix 8 is provided with a greater length of bi-metallic strip material than the helix 9 and when heated to the same temperature as the helix 9 will effect a greater "rotary movement of its end 19 in'one direction than will be effected by the helix 9 upon the prongs l5 carried at its free end; and since the prongs l5 are carried by the free end of the helix 9; the combined opposite rotary eifects of .heating the helices 8 and '9 simultaneously will be to move the prongs I5 114 a rotary path about the axis of the helices 8 and 9 an amount which represents the amount of rotary movement of the end I0 of the helix 8, which is in excess of that effected by the helix 9 upon the prongs l5.

Therefore, by the excess "of rotary movement effected by the helix 8, the prongs! 5 will be moved to carry the contact carrying arm I8 to move the contact 11 in a rotary path to effect engagement between the contact I1 and the fixedcontact 56, which is mounted on a post 68. Since engagement is had between the contacts 58-41, an

electrical circuit is closed which in the embodiment of Fig. 11 may be traced from the source of current S, such as a storage battery through v the closed switch SW, the indicator heating element 21, circuit conductor I [3, the connector post 89, the conductor 83, the controller heating element 54, the conductor 53, the supporting post 88, the contacts 5'6--l1, now in engagement, the arms l6 and 14, the prongs l5, the integrally joined helices 8 and 9 and thence through the grounded frame of the water jacket supporting the tubular support by its portion 2 to the grounded pole of the source of current S.

, Current flowing over the circuit just traced, will efiect simultaneous heating of the elements 21 and 54, at theindicator and controller, respectively, to cause a rotative movement, respectively, of the indicator hand 43, and the contact carrying arm l8. By supplying additional heat from the heating element 54, principally to the helix 9 and largely excluding the communication of heat therefrom, the helix 8 will cause the helix 9, although helix 9 is of shorter length and contains fewer convolutions and therefore is less responsive than the helix 8 when they are at the same tem- 4 aomevs perature, to respond additionally because of its increased temperature to move the prongs II in the opposite direction to that above described, in other words in a clockwise direction, as viewed 5 in Fig. 9, until theeontacts I1 and 88 are separated. Separation of these contacts will not occur until the heating element and the helix 8, taken together, have accumulated sufllcient heat, so that the ultimate temperature effected by the i helix 8 is sufllcient to cause it to respond thermostatically to move its free end sumciently to break the contacts. An appreciable period of heating is thereby effected and in addition, even after the instant when the contacts I146 are broken,

15 heat will continue to be supplied to the helix 8 from the heated element 54 even though it has started to lose some of its heat, so that the contacts l'|-56 will be. separated an appreciable distance, until the communication of heat to'the 20 helix 8 has become discontinued.

Since the circuit is thus broken, however, cooling of the heating element 8 will be eileetedgradually until the heat electrically eflected in the helix 8 will produce a lesser rotatlve effect than 25 that produced in the helix 8 by heat received from the fluid, and the contacts "-58 will be reclosed. This operation will be periodically continuous and will eilect a periodic closure of the contacts and resultant periodic. flows of current 30 through the two heating elements, which will be thus supplied with increments of heat periodically and simultaneously.

Both heating elements are so disposed and with their associated parts possess a suillcient ability to store heat, only partially lost during nonheating periods, whereby neither the, electrically heated controlling helix 8 nor controlled helix I 24 is greatly cooled during non-heating periods.

As a result the indicator hand 48 having taken a given position on its associate scale will osciliate but slightly from such position and the mass and material composing said heating element and its associated parts relative to theradiating surface thereof is made such that it may 4 be heated in a sufficiently short time to effect an indicator hand movement to indicates given temperature telegraphed from the controller and will substantially maintain such indication while the current over the electrical circuit is com- 50 mutated periodically by the contacts "-88.

' The adjustment screw 55 for the controller may be rotated to longitudinally move its carried contact 58 to vary the heat supplied to the helix 8 by the heating element 54 required to effect 65 disengagement of the contacts i1 and 88, whereby the heating value of the current supplied to the indicating unit for a given ambient temperature is varied and consequently the position of the hand 48 is correspondingly moved. The glass 6 tube 88 may be spirally grooved to receive in such groove the electrical resistance wire 54 to predetermine its length and position, or any other suitable means may be provided to insure this effect.

65 It will be understood that since the helix 8 of the controller is shorter than the helix 8, more heat will be required to be supplied to it by the electrical circuit conductor than the heat supplied to the helix 8 to'accomplish a given 70 movement of the contact ll. Also, heat from the I fluid will be transmitted to a considerable extent to the helix l, as well as the helix 8, subtracting by its effect on the helix 8, from the primary actuating movement effected on the contact H by Hheatingofthe helix 8. a

The helix 8, however, is given a suillclently greater number of turns, so as to overcome this mechanical handicap when heated by the fluid. so that actuationpf the contacts is assured.

The electrical heating element it supplies sufllcient heat to the helix 8, additional to that supplied from the fluid medium, so that the helix 8 becoming hotter than the helix 8 and maintained at a greater temperature, while the heating element 84 is heated, insures that the contact ll may be moved from engagement with the contact 88 {after heating of the element II has progressed for a predetermined'short tinie, during eac heating period.

It wi, be understood that for greater values of temperature of the liquid in the water jacket, or other fluid medium, the total length of heating periods in a given time, relative to non-heating periods, will be commensurably increased, so that the total amount of heat supplied to the heating element 21 in a given short time, that is the rate of heating of the element 11, will be increased It will be understood, also, that the indicator hand 48 will take variable positions commensurable with the intensity of the heat during each heating period andthe length of such heating period, and the relative length of heating periods to non-heating periods, that is to the rate of heating.

Referring now to Figs. 12 to 15, inclusive, whichshow an indicator mechanism which is another embodiment of my invention, operating substantially like that shown in Figs. 1 to 6, inclusive. In this embodiment, a pair of longitudinally aligned and spaced spirally-formed thermostatelements 65 and 66 are provided, joined together by a yoke 61 uniting their outer ends. The central portion of the spiral 68 is rigidly secured to a fixed hub I68 adjustably' rotatable in a heatinsulating support 8 8, and the central portion of the spiral 88 carries a hub 18, which is rotatably joumalied on-a journal pinll rigidly carried on a second support 12, which is preferably spaced from the support 68, both being preferably secured to opposite sides of a spacer II.

The indicator apparatus, so far described, is secured byits supporting spacer element I8 to a lateral wall of a tube I4, which in turn is car- ,ried by an end wall of a preferably metallic shal-,,

low cup I8, apertured at It to receive the end of the tube 14-, which is rigidly secured to the cup end wall by making a press ilt therewith and/or ,by'soldering the contiguous surfaces of the tube and cup end wall. The hub l8 projects by a reduced end 'l| into the cup I8, the inner surface of whose end wall is provided withdial containingfacing 18, having suitable dial scale divisions and indicating indicia therefor, shown at 18, said face being suitably apertured. as at 80, whereby the hub I0 may project therethrough.

A dial glass 8| is carried on the rim of the cup I8 and held in place by an inwardly flanged tubular clamping annulus 82 held in place by screws acme 7s t 5 spirals 05 and 99 are wound in opposite directions so that upon all ambient temperature conditions communicated alike to the two spirals, each will tend to effect a rotary movement to the hub ll but in opposite directions, and both being of the same length-to the same degree toneutralize or to compensate each other for ambient temperatures.

Upon the heating element 04 being energize by flow of current-therethrough under conditions, for instance like that shown in Fig..11, for the heating element 21, the inner surfaces of the convolutions of the bi-metallic convolutions of the spiral 66 being of the more expansible material, rotation of the hub TI carrying the indicator hand 80 will be effected to move the point of the hand over the scale 19 toward the right. The appa-' ratus, as described, is provided for the same purposes and, operates in the same manner as described in the embodiment for Figs. 1 to 6, in-

elusive.

In the embodiment of Figs. 14 and 15, a modification from that shown inFigs. 1 to 6, inclusive, is shown, whereby the heating element 21' telescoped within the helix- 24" is susceptible of being longitudinally adjusted by an adjusting screw 09 screwthreaded in an opening of the insulating base l8, and therefore, movable longitudinally by rotating it. In this embodiment, the heating element 21' includes a rod of glass or like material supported between the end'of the screw and the resilient heat insulating guard 26'.

From the above description, it will be under- 7 stood that rotation of the screw 89 will longitudinally displace the heating element relative to the convolutions of the thermostatic helix 24', and therefore vary the amount of heat communicated from the heat element to the convolutions of said helix.

This provides a manufacturing adjustment which may be substituted for the expedient of drawing some of the wire of the heating element,

' such as 21, Fig. 3, from the helix. In this embodiment, also, a sheet metalijrame is provided for supporting the relative parts-of the mechanism on the base l8, said framecomprising standards l9 adapted to support a dial plate, as that shown at 20, Figs. 3, 4, and 6, instead of the posts I9 shown/in Figs. 3 and 4. r

Figs. 16 to 18, inc1usive,.illustrate another embodiment indicator, which differs principally from that shown in Figglaand 15in that the bimetallic material pi'oviding a pair of relatively compensating thermostat elements 24" and 23" comprise only one convolution which is joined by an intermediate substantially V-shaped loop 25", which is stiffened longitudinally of the thermostats by bending it longitudinally, as shown at 80 and 9|, so that lateral warping in this part of thethermostat will not occur to any appreciable slot 94 -'into a supporting base 98 is effective to retain the unitary element comprising the plate 93, the thermostatic elements 24" and 23" and the hand 43" in a given rotative position of adjustment wherein the hand 43" takes a given position relative to the dial scale upon a given electrical energization imparted to its heating element 21".

Referring now to the embodiment of the controller shown in'Figs. 19" and 20, this embodiment is provided with elements generally. corresponding to those of the embodiment of Figs. '7 to 11,

inclusive, with the following exceptions. For the tube comprising stepped sections I, 2, and 3, a sheet metal tube 99 is provided to the end wall of which the fixed end of the bi-metallic helix 8' is aflixed, the tube 99 terminating in an enlarged cup portion I forming a part of the casing for the elements consisting'of the movable contact ll and the flxed contact 56. The fixed contact is carried on a post 54' secured by a stem IM to an inverted cup-shaped element I02 of insulating material, a reduced portion of whose tubular lateral walls I03 is telescoped snugly within the lateral walls of the cup-shaped end I00 of the tube 99.

Besides the thermostatic helix 8', an electrically heated helix"9', shorter in length and longitudinally aligned relative thereto, is provided as in the foregoing'embodiment referred to, and a preferably helical heating element 54' of resistance wire carried on a rod 50' is telescoped within the helix 9". The two helices 8' and 9' are joined at their adjacent ends by a yoke I 0 in the form of a wire rod. As in the foregoing case, the two helices are wound in opposition. The rod 50' is rigidly fixed within a central bore of the insulating cover cap I02. The cover cap I02 is bodily rotatable to. rotatably adjust the fixed contact 56 for engagement with the thermostatically movable contact II. A set screw I04 through the lateral wall of the cup shaped end of the tube 99 holds the insulating cover cap I02 in any desired adjusted position. The electrical heating element is joined by its two terminal circuit conductors to the fixed contact 54' and an electrical terminal element I05 consisting of a screw projected through the end wall of the cap I02 and a binding post nut disposed on the exterior side of the cap.

The device of Figs. 19 and 20 may be projected into any suitable opening in a wall of a fluid containing casing, or the entire device exposed to fluids, such as air, the temperature of disposed indicator, such as any of those herein shown connected in electrical serial circuit with the controller of Figs. 19 and 20, together with the source of current, as shown in Fig. 11.

Having thus described my invention in various embodiment apparatuses, I am aware that-numerous and extensive. departures may be made from the apparatuses herein illustrated and described, but without departing from the spirit of my invention.

7 I claim:

1. An electrothermal indicator comprising a pair of substantially longitudinally aligned helices of bi-metallic material, joined together by an end of each, a support, an indicator element,

the other end of one of said helices being secured to said support and the other end of the second ,helix being secured to said indicator element and an electrical heating element telescoped. within one of said helices extending longitudinally thereof and being supported coaxially thereof and communicating heat through intervening air space to the convolutions thereof, the other helix ,which is adapted to be indicated by a remotely 8 heated air from the electrical heating element to the compensating helix, said heating element b61118 supported by opposed portions of said shield and said'support.

2. In an electrical indicator comprising a coil .01 bi-metallic material having a fixed end and a free end, an indicator element supported by the free end and an electrical heating element extending longitudinally within the coil and imparting heat through the intervening air space thereto to operate said indicator element, and

means supporting said heating element for adjusting its length relative to that oi the said associated coil.

3. In an electrical indicator comprising a spiral 2 of bi-metallic material having a fixed end and a free end, an indicator-element supported by the free end and an electrical heating element extending longitudinally within the spiral and imparting heat through the intervening .space thereto to operate said indicator element, and

support means ior'said heating element adapted to relatively adjust the length of the heating element and its associated spiral portion.

4. In an electrical indicator comprising a spiral 01 iii-metallic. material having a fixed end and a free end, an' indicator element supported by the free endand an electrical heating element vextending longitudinally within the spiral and imparting heat through the intervening space thereto to operatesaid indicator element, and

means supporting saidheating element -i'or adjusting its length relative to the said associated spiral, said adjusting means comprising a-screwthreaded support and an element 01' the casing 40 carrying said support in relative screwthreaded relation. Y a

. 5. An electrical indicator comprising spaced coils of bi-me'tallic material, an end oi one 01 said 1 coils being fixed, the coils being intermediately ment having portions movable in opposite directions responsive to thermal changes, one end of said element being fixed to'a support and the' opposite end being ireely movable, an indicating element aflixed to said free end, electrical heating means associated with one of said portions, m'eans substantially shielding the other portion from the heating efiect oi the heating means, 6

ices oi bi-metallic material. joined together by 15 an end of each. a support, an indicator element. the other end of one of said helices being secured to said support and the other end oi. the second helix being secured'to said indicator element and an electrical heating elementv disposed in heat 2 exchanging relation to one of said helices, the other helix compensating the electrically heated helix for changes of ambient temperatures, and a shield interposed transversely between adjacent convolutions of the helices to obstruct the fiow of 25 heated air from the electrical heating element to the compensating helix, said heating element being supported by oppoud portions of said shield and said support. a

8. In an electrical indicator comprising a coil of bi-metallic material having a fixed end and a iree end, anindicator element supported by the free end and an electrical heating element so disposedas to be in heat exchanging relation to said coil to operate said indicator element, and means supporting said heating element for adjusting its lengthrelative to that of thetsaid as-. sociated coil. K

9. In an electrical indicator comprising a spiral ot'bi-metailic material having a fixed end and a 40 free end, an indicator element supported by the free end and an electrical heating element disposed in heat exchanging relation to said spiral to operate said indicator element, and support means ior said heating elementadapted to relatively adjust the length 01 the element and its associated spiral portion.

10.. In an electrical indicator comprising a spiral of bi-metallic material having a fixed end and a free end, an indicator element supported by the free end and an electrical heating element disposed in heat exchanging relationto said spiral and means supporting said heating element for adjusting its length relative to the said associated 9 ml, said adjusting means comprising a screwthreaded support and an element of the casing carrying said support in relative screwthreaded relation. V

v THEODORE J. BMULBKI.

e a he 

